[PATCH]: PROBLEM: Panic booting from USB disk in ioremap.c (line 81)

["Elliot Mackenzie" <macka@adixein.com>]

Kernel-devs:

This patch simply adds a sanity check to bootflag.c to detect a bad RSDT
pointer and avoids a kernel panic on boot with some buggy BIOSes.  The
patch is an "interim" patch, as we believe Len Brown has plans to use
the ACPI code to manage SBF in future.

Initial post:
>We have a problem booting vanilla 2.6.2 and 2.6.3 kernels from a USB
disk >(Transcend JetFlash, both 128MB USB 2 and 256MB USB 1). During
what appears >to be PCI device enumeration, we get the following panic:

Len Brown:
>bootflag.c should not use its own private ACPI table parser/mapper --
>this is a bug:
>http://bugme.osdl.org/show_bug.cgi?id=1922

This is an interim patch for anyone that is wrestling with the same
issue.  
Thank you to Randy Dunlap for his helpful assistance early in the
process (and for some of the code below).  

Kind regards,
Doug Turk and Elliot Mackenzie.


========================================================================
====
--- linux-2.6.3/arch/i386/kernel/bootflag.c	Wed Feb 18 13:59:06 2004
+++ linux-2.6.3-doug/arch/i386/kernel/bootflag.c	Tue Feb 24
23:18:51 2004
@@ -192,22 +192,37 @@
 	}
 	if(i>0xFFFE0)
 		return 0;
-		
-		
+
 	rsdt = ioremap(rsdtbase, rsdtlen);
 	if(rsdt == 0)
 		return 0;
-		
-	i = readl(rsdt + 4);
+
+	/* Check the RSDT signature */
+	if (memcmp(rsdt, "RSDT", 4))
+	{
+		iounmap(rsdt);
+		printk(KERN_WARNING "SBF: Could not map RSDT: bad
signature\n");
+		return 0;
+	}
+
 	
 	/*
 	 *	Remap if needed
 	 */
-	 
+	i = readl(rsdt + 4);
+
 	if(i > rsdtlen)
 	{
 		rsdtlen = i;
 		iounmap(rsdt);
+		/* Verify that the RSDT length is sane. */
+		if (rsdtlen > 0x1000) {	/* arbitrary for now */
+			printk(KERN_ERR "SBF: invalid rsdtlen = 0x%x\n",
+					rsdtlen);
+			return 0;
+		}
+
 		rsdt = ioremap(rsdtbase, rsdtlen);
 		if(rsdt == 0)
 			return 0;